1. Field of the Invention
The present invention relates to a color deleting apparatus for use in a digital color copying machine, a color facsimile machine, or the like, to delete color markings from an original document.
2. Description of the Prior Art
Recent digital color copying machines are equipped with various editing functions in addition to the original copying function to reproduce an original color document with high precision. One editing function is, for example, to color the original document copied by a conventional monochrome copying machine, or to change a specific color of the original document to a different color.
In addition to the above, there is a desire to change a copy from a color marked document to a non-color marked document. In other words, there is a desire to provide such a copying machine that when a document with color markings or with color stamps is set, a copied document with no color markings or no color stamps is reproduced. Such a color deleting function is desired to be added to the conventional copying machines so as to easily delete the chromatic area of the document except for the achromatic area.
The conventional copying machines have not been provided with the above-noted color deleting function by simply deleting the chromatic area from the document, but instead, the color deleting function is achieved by the use of the aforementioned color changing function, as explained below.
In FIG. 8, a block diagram of a prior art color image processing apparatus is shown, wherein reference numbers 201, 202, 203 and 204 represent an image reading means, a position indicating means, a detecting means and a color changing means, respectively.
The conventional color image processing apparatus shown in FIG. 8 operates in the following manner.
The image reading means 201 reads a color image of the original document using an image sensor such as a CCD (charge-coupled device), and outputs color data of decomposed three colors (digital data). The position indicating means 202 which is comprised of a digitizer and the like can input the positional data of a pixel at one arbitrary point by designating the one point within the area having an approximately constant density of the color image. The detecting means 203 detects the maximum and minimum values of the density of N.times.N pixels in the periphery of the pixel designated by the position indicating means 202 in the color data of three colors. The color changing means 204 compares the maximum and minimum values detected by the detecting means 203 with the color data of three colors supplied from the image reading means 201, thereby determining whether the pixel is within the area of the designated density, and changing the color of the area to a different color depending on the determining result. Accordingly, in the prior art color image processing apparatus, a color is deleted by indicating the color that is desired to be deleted from the original document and changing it to white. Such a copying machine is disclosed, for example, in Japanese Patent Laid-Open Publication 62-192862. Other prior art copying machines are disclosed in Japanese Patent Laid-Open Publication 62-131667 and in European Patent Publication EP 0,363,146 A2.
According to the aforementioned method, however, if a plurality of colors are desired to be deleted, the designation of the color should be repeatedly carried out one by one.
Moreover, only the color within the designated range of density which is between the maximum and minimum detected density can be deleted in the aforementioned method, and the color beyond the designated range cannot be deleted.
Furthermore, when the color copying machine is of a type which carries out four sequential copying operations of yellow, cyan, magenta and black images, the forming of a monochromatic copy takes a relatively long time.